Calendar Customization: Adding Appointment Status Types

The executives at my company, like most executives, live and die by their calendars. I've received a request to add custom appointment status types in addition to the standard set:

Free

Busy

Tentative

Out of Office

Unknown

For example, they're looking for the following additional status types:

Travel

Client Meeting

Vacation

Then, they can block time in their own calendars thereby providing that information to anyone that attempts to schedule them in a meeting. These status types would be readily visible in the 'Schedule' tab of a new appointment so that the meeting caller could instantly know the status of that potential attendee.

Does Zimbra provide the ability to add custom status types? Is this limited by the calendar standard?